How do I set up rate × time = distance problems?

[Hardeep]

I need help in understanding how to do these problems:

1. Tracy leaves for work at 8 A.M. traveling at 36 mph. Sarah finds that Tracy has forgotten her briefcase, so she leaves at 8:05 chasing after her at 50mph. At what time will Sarah catch Tracy?

2. Two jets leave St. Louis at 2 P.M., one traveling north at 850km/h and the other south at 750km/h. At what time will they be 4000km apart?

3. It takes a train 90min longer to go from Fartmington to Allentown at 60km/h than it does to return at 80km/h. What is the distance between these towns?

These are the "rate x time = distance" problems. How do I figure out what goes where?

 

[Diane_]

1) There are a couple of ways to work this one. Think of it this way: Sarah is traveling 14 miles per hour faster than Tracy. Figure out how far ahead of Sarah Tracy is (distance = rate x time), then figure out how long it would take Sarah to travel that distance at 14 miles per hour (time = distance/rate)

2) They are traveling at a relative 1600 km/hr (850 + 750). How far would something go traveling that fast?

3) Relative rates again. What is the difference in their speeds, and how far can you travel in 90 minutes (watch the units) at that speed?

Hope this helps.

 

[Hypercase]

Graphing always helps make the situation clear. try it.

 

[Hardeep]

I kinda get #1, would I be like x+5=14?